1. Field of the Invention
This invention relates to a phosphate-reduced detergent consisting of several granular powder components and containing finely-divided crystalline zeolites, nonionic surfactants selected from the group consisting of polyglycolether derivatives, anionic surfactants, and homopolymeric or copolymeric carboxylic acids as its essential constituents, and optionally sodium tripolyphosphate, in a particular powder distribution.
2. Discussion of Related Art
Finely-divided zeolites of the NaA and NaX type have been repeatedly proposed as phosphate substitutes in detergent compositions. However, it has been found that they must be present in the detergent in quantities of at least 20% by weight, and preferably in quantities of at least 25% by weight, in order to obtain a good detergent effect and, in particular, to minimize fabric incrustation. Unfortunately, considerable problems are involved in incorporating quantities as large as these in a detergent composition by spray drying. In the interests of energy conservation and efficient utilization of the hot spray drying towers, it is desirable to keep the water content of the mixture to be spray-dried as low as possible. The mixtures to be spray-dried normally contain from 30 to at most 45% by weight water, of which from 8 to 15% by weight remains in the product after spray drying. The synthetic zeolites are generally processed in the form of a filter-moist, stabilized suspension containing about 50% water which is particularly suitable for further processing. The addition of further, sprayable detergent constituents frequently containing water may then lead to a further increase in the water content of the slurry and, hence, to an increased energy demand and to a loss of capacity in the spray-drying plants.
If the zeolite is added to the slurry as a predried powder in order o reduce the water content of the slurry, zeolite agglomerates may be formed which tend to deposit on the textiles during the washing process. These problems may especially occur when the compositions contain water-soluble silicates like sodium waterglass.
Additional problems arise during spray-drying of phosphate-reduced washing compositions. As it is known, a certain percentage of the tripolyphosphate incorporated into the slurry is hydrolyzed to orthophosphate and pyrophosphate in the course of the spray drying process. These hydrolyzed phosphates favor the formation of incrustations on the washed textiles. It has been found that with decreasing phosphate content in the composition, the portion of the undesirable ortho- and pyrophosphates increases to the disadvantage of the tripolyphosphate content. Therefore, particularly in low-phosphate compositions the portion of the phosphates that induce incrustation is particularly high. Removing the phosphate from the spraying process and post-dosing it to the separately prepared powder will create new problems, especially if also the zeolite is not processed via spray-drying. In this case, the amount of inorganic carrier substance in the slurry would be too low with respect to the organic ingredients. Thus, the risk of dust explosions in the hot spray tower would increase and the formation of dry, free-flowing beads would be made more difficult.
Another problem is created by the use of nonionic surfactants. These compounds, which are distinguished by very high detergency, undesirably increase the viscosity of the spray-dried slurry where anionic surfactants are simultaneously present. In addition, they give rise to aerosol formation, so-called "pluming", in the offgases from the spray-drying tower. According to German Application No. 22 04 842-A 1, the nonionic surfactants are applied to a carrier powder which contains, inter alia, bentonite and microfine silicon dioxide, a particularly effective binder. This premix may then be added to a spray-dried detergent powder. However, silicon dioxide is not a washing-active constituent, i.e., it merely results in additional costs and makes no contribution to the detergent effect. The premix is prepared by granulating the powder-form carriers with the liquid or molten nonionic surfactant. The production of uniform granulates having a defined grain spectrum and powder density by this process involves considerable difficulties. Accordingly, mixtures of these granulates with spray-drying powders of low specific gravity also have a more or less irregular grain spectrum and show a tendency towards separation.
According to German Application No. 25 07 926-B 1, finely-divided crystalline aluminosilicates which, in regard to their composition include zeolites of the NaA and NaX type, are proposed for use as carrier material for the nonionic surfactants. In this case, too, the starting material used is a powder-form zeolite. There is nothing in this literature reference either to suggest that, to prepare this premix, it is necessary to start out with a prepared granulate having a certain grain specification and, as described hereinafter, certain additives and quantitative ratios in order to avoid subsequent separation of the granulate and to obtain optimal detergent properties.
A detergent product consisting of three powder-form or granular powder components is known from German Application No. 27 53 680 A2. The first powder component consists of a spray-dried powder and contains anionic and/or nonionic surfactants, builder salts, including phosphates, zeolites, alkali metal silicates and carbonates. The second component consists of builder salts serving as carrier material and silicone foam inhibitors adsorbed thereon. The third component consists of a granulate prepared from perborate or another per compound and one or more builders, preferably phosphates, using nonionic surfactants as binder. However, the uptake capacity of perborate for nonionic surfactants is very limited, although this is not critical in the present case because the third powder component only performs the function of improving the wetting properties and, hence, the flush-in behavior of the powder mixture in washing machines. However, relatively small amounts of nonionic surfactant or of the third powder component are sufficient for this purpose. The notion of using a prepared, phosphate-free carrier granulate which, by virtue of its special composition and method of production, is capable of taking up large amounts of nonionic surfactants is foreign to this publication. In addition, there is nothing in the cited application to show how the aluminosilicates, polycarboxylates and surfactants optionally used should be distributed among the individual powder components in order to obtain optimal detergency with phosphate-free detergents.
The object of the present invention is to solve the following problems or to bring a solution nearer to fruition.
1. Providing a phosphate-reduced detergent which is comparable with a conventional phosphate-containing detergent in its soil removal, i.e., primary detergency, and incrustation prevention, i.e., secondary detergency. PA1 2. Decreasing the hydrolyzing rate of the tripolyphosphate (if present) and reducing the amount of organic compounds in the slurry and the hot spraying tower. PA1 3. Increasing the percentage of zeolite in the detergent while, at the same time, easing the load on the spray-drying towers and avoiding an excessive energy demand. PA1 4. Avoiding the formation of zeolite agglomerates. PA1 5. Developing a carrier material having a high abrasive resistance and being completely dispersible in water without forming coarse particles, which carrier material is capable of taking up large amounts of nonionic surfactants and of increasing the percentage of zeolite in the final detergent and converting it into a premix which, by virtue of its grain spectrum, is suitable for mixing with a spray-dried powder. PA1 6. Influencing the weight per liter of the final detergent by correspondingly formulating the premix with the object of reducing the packing volume by increasing the weight per liter of the product. PA1 7. Improving the powder properties in regard to grain strength and dust formation, avoiding separation, obtaining good flow properties both immediately after production and also after storage for several months and obtaining favorable disintegration and dissolving properties on introduction into the wash liquor and on flushing into the washing machine with cold tapwater. PA1 8. Maintaining the suitability of the multicomponent mixtures for taking up further powder components, for example those containing bleaches, per-acid precursors, enzymes and foam inhibitors.